All my iTunes songs and Playlists are gone!!

ok firstly I apologize is this is a repost. I've searched through the forums and I can't find an answer.

So I'm using iTunes 9.2.1 and I hadn't noticed any issues but then today for no reason at all when I connected my ipod touch to my computer to charge it, iTunes opened (as normal) and all my music was missing along with all my playlists. Why did this happen & does anyone know a fix for this?? I checked my HDD#2 (where all my music is located) and it's all there...

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